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S. Shen

Publications and source records attributed to S. Shen.

At least 19 recordsLinked to original sources
arXiv2025

Mechanically Reconfigurable GRIN Lens Concept for Focusing and Beamforming Applications

This study presents a prospective concept of a mechanically reconfigurable Gradient Index (GRIN) lens for focusing and beamforming applications. The lens is formed by corrugated layers, each realizing a refractive index profile expressed in a basis of Chebyshev polynomials. The focal point position is controlled by shifting the GRIN lens layers. A geometrical optics-based approach is implemented for the three scenarios of focusing at varying focal distance. The geometrical optics results are validated by numerical simulations, with some discrepancies observed due to modeling approximations and structural granularity. We also discuss scalability of the proposed concept for operation at infrared wavelengths.

physics.optics↗
arXiv2025

Outflowing shocked gas dominates the NIR H$_2$ emission from the dual AGN NGC6240

[Abridged] We present a multi-line study of the kinematics of the molecular and ionised gas phases in the central 2 kpc of NGC6240, based on JWST/NIRSpec and ALMA observations. We devised a new spectral-line fitting approach to de-blend rotating and non-rotating gas components, which is better tailored to the extreme feedback mechanisms at work in NGC6240. We find that ~65% of the Pa$\alpha$, H$_2$, and [FeII] line fluxes within the NIRSpec field of view arise from gas components that are kinematically decoupled from the stars. The NIR H$_2$ lines show the most deviation from the stars, with peak emission between the two rotating stellar structures. The PAH 3.3$\mu$m feature does not follow the NIR H$_2$ morphology, indicating that the latter does not trace PDRs. In the non-rotating gas components, we identify a biconical wind launched from the northern AGN, expanding along the minor axis of stellar rotation. This wind is dominated by ionised gas and, although it entrains some H$_2$, it does not show a H$_2$/PAH enhancement, suggesting either high UV irradiation or expansion along a relatively gas-free path. Furthermore, we find bright non-rotating gas emission between the two AGN and around the southern AGN, which we interpret as due to an outflow launched from the southern nucleus, coinciding with the molecular outflow previously studied in cold (sub-)millimeter tracers. The strong H$_2$/PAH enhancement measured in this region, coextensive with high velocity redshifted gas ($v\sim900$ km s$^{-1}$), suggests that the shocks responsible for the high H$_2$/PAH ratios are due to the outflow rather than to the collision of media during the merger. Our results show that the bulk of the NIR line emission in NGC6240 is decoupled from the stars, and that most of the warm H$_2$ is shock-excited and embedded in a powerful outflow, where it coexists with colder molecular gas.

astro-ph.GA↗
arXiv2025

DashChat: Interactive Authoring of Performance Dashboard Design Prototypes through Conversation with LLM-Powered Agent

Performance dashboards are dashboards designed for and deployed within industrial settings (e.g., enterprises, government agencies) to showcase and monitor their operational performance. They have evolved into an important and well-commercialized format for data visualization. In practice, the ideation and negotiation phases demand rapid prototyping and iteration to align with evolving client needs. However, existing tools compel designers to compromise either on iteration speed or on the meticulous handling of visual complexities. To address these gaps, we introduce DashChat for generating performance dashboard prototypes. Collaborating with industry experts, we derived the design requirements and analyzed 114 dashboards to extract common design patterns. Informed by the findings, our solution integrates a chat interface with an LLM-driven multi-agent pipeline, translating textual requirements into prototypes. We evaluated the system by comparing it with a baseline, demonstrating its effectiveness in facilitating the prototyping process while ensuring design quality.

cs.HC↗
arXiv2024

Molecular gas scaling relations for local star-forming galaxies in the low-$M_*$ regime

We derived molecular gas fractions ($f_\mathrm{mol}=M_\mathrm{mol}/M_*$) and depletion times ($\tau_\mathrm{mol}= M_\mathrm{mol}/\mathrm{SFR} $) for 353 galaxies representative of the local star-forming population with $10^{8.5}\,M_\odot < M_* < 10^{10.5}\,M_\odot$ drawn from the ALLSMOG and xCOLDGASS surveys of CO(2-1) and CO(1-0) line emission. By adding constraints from low-mass galaxies and upper limits for CO non-detections, we find the median molecular gas fraction of the local star-forming population to be constant at $\log f_\mathrm{mol}=-0.99^{+0.22}_{-0.19}$, challenging previous reports of increased molecular gas fractions in low-mass galaxies. Above $M_*\sim 10^{10.5}\,M_\odot$, we find the $f_\mathrm{mol}$ vs. $M_*$ relation to be sensitive to the selection criteria for star-forming galaxies. We tested the robustness of our results against different prescriptions for the CO-to-H$_2$ conversion factor and different selection criteria for star-forming galaxies. The depletion timescale $\tau_\mathrm{mol}$ weakly depends on $M_*$, following a power law with a best-fit slope of $0.16\pm 0.03$. This suggests that small variations in specific SFR ($ \mathrm{sSFR=SFR}/M_*$) across the local main sequence of star-forming galaxies with $M_* < 10^{10.5}\,M_\odot$ are mainly driven by differences in the efficiency of converting the available molecular gas into stars. We tested these results against a possible dependence of $f_\mathrm{mol}$ and $\tau_\mathrm{mol}$ on the surrounding (group) environment of the targets by splitting them into centrals, satellites, and isolated galaxies, and find no significant variation between these populations. We conclude that the group environment is unlikely to have a large systematic effect on the molecular gas content of star-forming galaxies in the local Universe.

astro-ph.GA↗
arXiv2023

A sensitive APEX and ALMA CO(1-0), CO(2-1), CO(3-2), and [CI](1-0) spectral survey of 40 local (U)LIRGs

We present a high sensitivity spectral line survey of CO(1-0), CO(2-1), CO(3-2) and [CI](1-0) in 40 local (ultra) luminous infrared galaxies ((U)LIRGs), all with previous Herschel OH119 $\mu$m observations. We use single-dish observations (PI and archival) conducted with APEX, complemented with ALMA and ACA data. We study the total emission and pay special attention to the extended low-surface brightness components. We find a tight correlation between low-J CO and [CI] line luminosities suggesting their emission arise from similar regions, at least when averaged over galactic scales. We estimate a median CO-to-H$_2$ conversion factor of $1.7\pm 0.5$ M$_{\odot}$ (K km s$^{-1}$ pc$^2)^{-1}$ for ULIRGs, using [CI] as an independent tracer. We derive median galaxy-integrated CO line ratios ($r_{21}$, $r_{31}$ and $r_{32}$), as well as $r_{CICO}$, significantly higher than normal star forming galaxies, confirming the exceptional molecular gas properties of ULIRGs. We find that $r_{21}$ and $r_{32}$ are poor tracers of CO excitation in ULIRGs, while $r_{31}$ shows a positive trend with $L_{IR}$ and SFR, and a negative trend with the H$_2$ gas depletion timescales ($\tau_{dep}$). When studying CO line ratios as a function of gas kinematics, we find a positive relation between $r_{21}$ and $\sigma_v$, which can be explained by CO opacity effects. We find that the linewidths of [CI] lines are ~10% narrower than CO lines, which may suggest that the low optical depth of [CI] can challenge its detection in diffuse, low-surface brightness outflows, and so its use as a tracer of CO-dark H$_2$ gas in these components. Finally, we find that higher $L_{AGN}$ are associated to longer $\tau_{dep}$, consistent with the hypothesis that AGN feedback may reduce the efficiency of star formation.

astro-ph.GA↗
arXiv2023

New experimental constraint on the $^{185}$W($n,\gamma$)$^{186}$W cross section

In this work, we present new data on the $^{182,183,184}$W($\gamma,n$) cross sections, utilizing a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility. Further, we have extracted the nuclear level density and $\gamma$-ray strength function of $^{186}$W from data on the $^{186}$W($\alpha,\alpha^\prime\gamma$)$^{186}$W reaction measured at the Oslo Cyclotron Laboratory. Combining previous measurements on the $^{186}$W($\gamma,n$) cross section with our new $^{182,183,184}$W($\gamma,n$) and ($\alpha,\alpha^\prime\gamma$)$^{186}$W data sets, we have deduced the $^{186}$W $\gamma$-ray strength function in the range of $1 < E_\gamma < 6$ MeV and $7 < E_\gamma < 14$ MeV. Our data are used to extract the level density and $\gamma$-ray strength functions needed as input to the nuclear-reaction code \textsf{TALYS}, providing an indirect, experimental constraint for the $^{185}$W($n,\gamma$)$^{186}$W cross section and reaction rate. Compared to the recommended Maxwellian-averaged cross section (MACS) in the KADoNiS-1.0 data base, our results are on average lower for the relevant energy range $k_B T \in [5,100]$ keV, and we provide a smaller uncertainty for the MACS. The theoretical values of Bao \textit{et al.} and the cross section experimentally constrained on photoneutron data of Sonnabend \textit{et al.} are significantly higher than our result. The lower value by Mohr \textit{et al.} is in very good agreement with our deduced MACS. Our new results could have implications for the $s$-process and in particular the predicted $s$-process production of $^{186,187}$Os nuclei.

nucl-ex↗
arXiv2021

DeepDDS: deep graph neural network with attention mechanism to predict synergistic drug combinations

Drug combination therapy has become a increasingly promising method in the treatment of cancer. However, the number of possible drug combinations is so huge that it is hard to screen synergistic drug combinations through wet-lab experiments. Therefore, computational screening has become an important way to prioritize drug combinations. Graph neural network have recently shown remarkable performance in the prediction of compound-protein interactions, but it has not been applied to the screening of drug combinations. In this paper, we proposed a deep learning model based on graph neural networks and attention mechanism to identify drug combinations that can effectively inhibit the viability of specific cancer cells. The feature embeddings of drug molecule structure and gene expression profiles were taken as input to multi-layer feedforward neural network to identify the synergistic drug combinations. We compared DeepDDS with classical machine learning methods and other deep learning-based methods on benchmark data set, and the leave-one-out experimental results showed that DeepDDS achieved better performance than competitive methods. Also, on an independent test set released by well-known pharmaceutical enterprise AstraZeneca, DeepDDS was superior to competitive methods by more than 16\% predictive precision. Furthermore, we explored the interpretability of the graph attention network, and found the correlation matrix of atomic features revealed important chemical substructures of drugs. We believed that DeepDDS is an effective tool that prioritized synergistic drug combinations for further wet-lab experiment validation.

cs.LG↗
arXiv2021

Magnetorotational instability with smoothed particle hydrodynamics

We present a thorough numerical study on the MRI using the smoothed particle magnetohydrodynamics method (SPMHD) with the geometric density average force expression (GDSPH). We perform shearing box simulations with different initial setups and a wide range of resolution and dissipation parameters. We show, for the first time, that MRI with sustained turbulence can be simulated successfully with SPH, with results consistent with prior work with grid-based codes. In particular, for the stratified boxes, our simulations reproduce the characteristic butterfly diagram of the MRI dynamo with saturated turbulence for at least 100 orbits. On the contrary, traditional SPH simulations suffer from runaway growth and develop unphysically large azimuthal fields, similar to the results from a recent study with mesh-less methods. We investigated the dependency of MRI turbulence on the numerical Prandtl number in SPH, focusing on the unstratified, zero net-flux case. We found that turbulence can only be sustained with a Prandtl number larger than $\sim$2.5, similar to the critical values of physical Prandtl number found in grid-code simulations. However, unlike grid-based codes, the numerical Prandtl number in SPH increases with resolution, and for a fixed Prandtl number, the resulting magnetic energy and stresses are independent of resolution. Mean-field analyses were performed on all simulations, and the resulting transport coefficients indicate no $\alpha$-effect in the unstratified cases, but an active $\alpha\Omega$ dynamo and a diamagnetic pumping effect in the stratified medium, which are generally in agreement with previous studies. There is no clear indication of a shear-current dynamo in our simulation, which is likely to be responsible for a weaker mean-field growth in the tall, unstratified, zero net-flux simulation.

astro-ph.GA↗
arXiv2021

The star formation history of Eridanus II: on the role of SNe feedback in the quenching of ultra-faint dwarf galaxies

Eridanus II (EriII) is an ultra-faint dwarf (UFD) galaxy (M_V=-7.1) located at a distance close to the Milky Way virial radius. Early shallow color-magnitude diagrams (CMD) indicated that it possibly hosted an intermediate-age or even young stellar population, which is unusual for a galaxy of this mass. In this paper, we present new ACS/HST CMDs reaching the oldest main sequence turnoff with excellent photometric precision, and derive a precise star formation history (SFH) for this galaxy through CMD-fitting. This SFH shows that the bulk of the stellar mass in Eri II formed in an extremely short star formation burst at the earliest possible time. The derived star formation rate profile has a width at half maximum of 500 Myr and reaches a value compatible with null star formation 13 Gyr ago. However, tests with mock stellar populations and with the CMD of the globular cluster M92 indicate that the star formation period could be shorter than 100 Myr. From the quantitative determination of the amount of mass turned into stars in this early star formation burst (~2x10^5 Msun) we infer the number of SNe events and the corresponding energy injected into the interstellar medium. For reasonable estimates of the EriII virial mass and values of the coupling efficiency of the SNe energy, we conclude that EriII could be quenched by SNe feedback alone, thus casting doubts on the need to invoke cosmic reionization as the preferred explanation for the early quenching of old UFD galaxies.

astro-ph.GA↗
arXiv2020

Inverse flexoelectret effect: bending dielectrics by a uniform electric field

It is highly desirable to discover an electromechanical coupling that allows a dielectric material to generate curvature in response to a uniform electric field, which would add a new degree of freedom for designing actuators. Flexoelectricity, a two-way coupling between polarization and strain gradient, is a good candidate. But its applications are usually limited to the nanoscale due to its inherent size dependence. Here, an inverse flexoelectret effect in silicone elastomers is introduced to overcome this limitation. Based on this idea, a flexing actuator which can generate large curvature at the millimeter length scale is fabricated and shown to have excellent actuation performance comparable with current nanoscale flexoelectric actuators. Theoretical analysis indicates that the new phenomenon originates from the interplay of electrets and Maxwell stress. This work opens an avenue for applying macroscopic flexoelectricity in actuators and flexible electronics.

cond-mat.soft↗
arXiv2019

Harmonic potential theorem: \\extension to spin-, velocity- and density-dependent interactions

One of the few exact results for the description of the time-evolution of an inhomogeneous, interacting many-particle system is given by the Harmonic Potential Theorem (HPT). The relevance of this theorem is that it sets a tight constraint on time-dependent many-body approximations. In this contribution, we show that the original formulation of the HPT is valid also for the case of spin-, velocity- and density-dependent interactions. This result is completely general and relevant, among the rest, for nuclear structure theory both in the case of ab initio and of more phenomenological approaches. As an example, we report on a numerical implementation by testing the small-amplitude limit of the time-dependent Hartree-Fock -- also known as Random Phase Approximation (RPA) -- for the translational frequencies of a neutron system trapped in a harmonic potential.

nucl-th↗
arXiv2018

Spatially resolved star formation and dust attenuation in Mrk848: Comparison of the integral field spectra and the UV-to-IR SED

We investigate the star formation history and the dust attenuation in the galaxy merger Mrk848. Thanks to the multiwavelength photometry from the ultraviolet (UV) to the infrared (IR), and MaNGA's integral field spectroscopy, we are able to study this merger in a detailed way. We divide the whole merger into the core and tail regions, and fit both the optical spectrum and the multi-band spectral energy distribution (SED) to models to obtain the star formation properties for each region respectively. We find that the color excess of stars in the galaxy $E(B-V)_s^{SED}$ measured with the multi-band SED fitting is consistent with that estimated both from the infrared excess (the ratio of IR to UV flux) and from the slope of the UV continuum. Furthermore, the reliability of the $E(B-V)_s^{SED}$ is examined with a set of mock SEDs, showing that the dust attenuation of the stars can be well constrained by the UV-to-IR broadband SED fitting. The dust attenuation obtained from optical continuum $E(B-V)_s^{spec}$ is only about half of $E(B-V)_s^{SED}$. The ratio of the $E(B-V)_s^{spec}$ to the $E(B-V)_g$ obtained from the Balmer decrement is consistent with the local value (around 0.5). The difference between the results from the UV-to-IR data and the optical data is consistent with the picture that younger stellar populations are attenuated by an extra dust component from the birth clouds compared to older stellar populations which are only attenuated by the diffuse dust. Both with the UV-to-IR SED fitting and the spectral fitting, we find that there is a starburst younger than 100~Myr in one of the two core regions, consistent with the scenario that the interaction-induced gas inflow can enhance the star formation in the center of galaxies.

astro-ph.GA↗
arXiv2017

Optimal Orientations of Quartz Crystals for Bulk Acoustic Wave Resonators with the Consideration of Thermal Properties

Piezoelectric crystals are widely used for acoustic wave resonators of different functioning modes and types including BAW and SAW. It is well-known that only some special orientations of crystals will exhibit desirable properties such as mode couplings, thermal sensitivity, acceleration sensitivity, and others that are important in design and applications of resonators. With extensive studies on physical properties in last decades and increasing industrial needs of novel products, it is necessary to comb the known knowledge of quartz crystal material for novel orientations and better products as agendas in the industry. With known material properties like elastic, piezoelectric, dielectric, and thermal constants, we can establish the relationships between vibrations and bias fields such as temperature to ensure a resonator immunizing from excessive response to changes causing significant degradation of resonator properties and performances. Since the theoretical framework of wave propagation in piezoelectric solids is known, we need to use the existing data and results for the validation of current orientations in actual products. The agreement will give us needed confidence of the theory and analytical procedures. Through rotations, we calculated physical properties as functions of angles and bias fields, enabling the calculation of resonator properties for the identification of optimal cuts. Such a procedure can also be applied to similar crystals for a careful examination of possible orientations to maximize the potential use of materials in acoustic wave resonators.

cond-mat.mtrl-sci↗
arXiv2016

Effect of local and large-scale environments on nuclear activity and star formation

Active galactic nuclei (AGN) is one of the main drivers for transition from star-forming disk to passive spheroidal galaxies. However, the role of large-scale environment versus one-on-one interactions in triggering different types of AGN is still uncertain. We present a statistical study of the prevalence of the nuclear activity in isolated galaxies and physically bound isolated pairs. For the purpose of this study we considered optically and radio selected nuclear activity types. We aim to assess the effect of one-on-one interaction on the fraction of AGN and the role of their large-scale environment. To study the effect of one-on-one interaction on the fraction of AGN in isolated galaxy pairs, we compare with a sample of isolated galaxies homogeneously selected under the same isolation criterion. We examine the effect of the large-scale environment by comparing with control samples of single galaxies and galaxy pairs. In general we found no difference in the prevalence of optical AGN for the considered samples. For massive galaxies, the fraction of optical AGN in isolated galaxies is slightly higher than that in control samples. Also the fraction of passives in high mass isolated galaxies is smaller than in any other sample. Generally, there is no dependence on optical nuclear activity with local environment. On the other hand, we found evidence that radio AGN are strongly affected by the local environment. Optical AGN phenomenon is related to cold gas accretion, while radio AGN is related to hot gas accretion. In this context, there is more cold gas, fueling the central optical AGN, in isolated systems. Our results are in agreement with a scenario where cold gas accretion by secular evolution is the main driver of optical AGN, while hot gas accretion and one-on-one interactions are the main drivers of radio AGN activity.

astro-ph.GA↗
arXiv2016

The MaGICC Baryon Cycle: The Enrichment History of Simulated Disc Galaxies

Using cosmological galaxy formation simulations from the MaGICC project, spanning more than three magnitudes in stellar mass (~10^7-3x10^{10} Msun), we trace the baryonic cycle of infalling gas from the virial radius through to its participation in the star formation process. An emphasis is placed upon the temporal history of chemical enrichment during its passage through the corona and CGM. We derive the distributions of time between gas crossing the virial radius and being accreted to the star forming region (which allows mixing within the corona), as well as the time between gas being accreted to the star forming region and then forming stars (which allows mixing within the disc). Significant numbers of stars are formed from gas that cycles back through the hot halo after first accreting to the star forming region. Gas entering high mass galaxies is pre-enriched in low mass proto-galaxies prior to entering the virial radius of the central progenitor, with only small amounts of primordial gas accreted, even at high redshift (z~5). After entering the virial radius, significant further enrichment occurs prior to the accretion of the gas to the star forming region, with gas that is feeding the star forming region surpassing 0.1Z by z=0. Mixing with halo gas, itself enriched via galactic fountains, is thus crucial in determining the metallicity at which gas is accreted to the disc. The lowest mass simulation (Mvir~2x10^{10}Msun, with M*~10^7Msun), by contrast, accretes primordial gas through the virial radius and onto the disc at all times. Much like the classical analytical solutions to the `G-dwarf problem', overproduction of low-metallicity stars is ameliorated by the inefficiency of star formation. Finally, gas outflow/metal removal rates from star forming regions as a function of galactic mass are presented.

astro-ph.CO↗
arXiv2016

The SDSS-IV extended Baryon Oscillation Spectroscopic Survey: selecting emission line galaxies using the Fisher discriminant

We present a new selection technique of producing spectroscopic target catalogues for massive spectroscopic surveys for cosmology. This work was conducted in the context of the extended Baryon Oscillation Spectroscopic Survey (eBOSS), which will use ~200 000 emission line galaxies (ELGs) at 0.6<zspec<1.0 to obtain a precise baryon acoustic oscillation measurement. Our proposed selection technique is based on optical and near-infrared broad-band filter photometry. We used a training sample to define a quantity, the Fisher discriminant (linear combination of colours), which correlates best with the desired properties of the target: redshift and [OII] flux. The proposed selections are simply done by applying a cut on magnitudes and this Fisher discriminant. We used public data and dedicated SDSS spectroscopy to quantify the redshift distribution and [OII] flux of our ELG target selections. We demonstrate that two of our selections fulfil the initial eBOSS/ELG redshift requirements: for a target density of 180 deg^2, ~70% of the selected objects have 0.6<zspec<1.0 and only ~1% of those galaxies in the range 0.6<zspec<1.0 are expected to have a catastrophic zspec estimate. Additionally, the stacked spectra and stacked deep images for those two selections show characteristic features of star-forming galaxies. The proposed approach using the Fisher discriminant could, however, be used to efficiently select other galaxy populations, based on multi-band photometry, providing that spectroscopic information is available. This technique could thus be useful for other future massive spectroscopic surveys such as PFS, DESI, and 4MOST.

astro-ph.GA↗
arXiv2015

Isolated Galaxies versus Interacting Pairs with MaNGA

We present preliminary results of the spectral analysis on the radial distributions of the star formation history in both, a galaxy merger and a spiral isolated galaxy observed with MaNGA. We find that the central part of the isolated galaxy is composed by older stellar population ($\sim$2 Gyr) than in the outskirts ($\sim$7 Gyr). Also, the time-scale is gradually larger from 1 Gyr in the inner part to 3 Gyr in the outer regions of the galaxy. In the case of the merger, the stellar population in the central region is older than in the tails, presenting a longer time-scale in comparison to central part in the isolated galaxy. Our results are in agreement with a scenario where spiral galaxies are built from inside-out. In the case of the merger, we find evidence that interactions enhance star formation in the central part of the galaxy.

astro-ph.GA↗